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                        <h1 id="iterator%E5%92%8Cfor-of%E5%BE%AA%E7%8E%AF">Iterator&#x548C;for...of&#x5FAA;&#x73AF;</h1>
<h2 id="iterator%EF%BC%88%E9%81%8D%E5%8E%86%E5%99%A8%EF%BC%89">Iterator&#xFF08;&#x904D;&#x5386;&#x5668;&#xFF09;</h2>
<p>&#x904D;&#x5386;&#x5668;&#xFF08;Iterator&#xFF09;&#x662F;&#x4E00;&#x79CD;&#x63A5;&#x53E3;&#x89C4;&#x683C;&#xFF0C;&#x4EFB;&#x4F55;&#x5BF9;&#x8C61;&#x53EA;&#x8981;&#x90E8;&#x7F72;&#x8FD9;&#x4E2A;&#x63A5;&#x53E3;&#xFF0C;&#x5C31;&#x53EF;&#x4EE5;&#x5B8C;&#x6210;&#x904D;&#x5386;&#x64CD;&#x4F5C;&#x3002;&#x5B83;&#x7684;&#x4F5C;&#x7528;&#x6709;&#x4E24;&#x4E2A;&#xFF0C;&#x4E00;&#x662F;&#x4E3A;&#x5404;&#x79CD;&#x6570;&#x636E;&#x7ED3;&#x6784;&#xFF0C;&#x63D0;&#x4F9B;&#x4E00;&#x4E2A;&#x7EDF;&#x4E00;&#x7684;&#x3001;&#x7B80;&#x4FBF;&#x7684;&#x63A5;&#x53E3;&#xFF0C;&#x4E8C;&#x662F;&#x4F7F;&#x5F97;&#x5BF9;&#x8C61;&#x7684;&#x5C5E;&#x6027;&#x80FD;&#x591F;&#x6309;&#x67D0;&#x79CD;&#x6B21;&#x5E8F;&#x6392;&#x5217;&#x3002;&#x5728;ES6&#x4E2D;&#xFF0C;&#x904D;&#x5386;&#x64CD;&#x4F5C;&#x7279;&#x6307;for...of&#x5FAA;&#x73AF;&#xFF0C;&#x5373;Iterator&#x63A5;&#x53E3;&#x4E3B;&#x8981;&#x4F9B;for...of&#x5FAA;&#x73AF;&#x4F7F;&#x7528;&#x3002;</p>
<p>&#x904D;&#x5386;&#x5668;&#x63D0;&#x4F9B;&#x4E86;&#x4E00;&#x4E2A;&#x6307;&#x9488;&#xFF0C;&#x6307;&#x5411;&#x5F53;&#x524D;&#x5BF9;&#x8C61;&#x7684;&#x67D0;&#x4E2A;&#x5C5E;&#x6027;&#xFF0C;&#x4F7F;&#x7528;next&#x65B9;&#x6CD5;&#xFF0C;&#x5C31;&#x53EF;&#x4EE5;&#x5C06;&#x6307;&#x9488;&#x79FB;&#x52A8;&#x5230;&#x4E0B;&#x4E00;&#x4E2A;&#x5C5E;&#x6027;&#x3002;next&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x5305;&#x542B;value&#x548C;done&#x4E24;&#x4E2A;&#x5C5E;&#x6027;&#x7684;&#x5BF9;&#x8C61;&#x3002;&#x5176;&#x4E2D;&#xFF0C;value&#x5C5E;&#x6027;&#x662F;&#x5F53;&#x524D;&#x904D;&#x5386;&#x4F4D;&#x7F6E;&#x7684;&#x503C;&#xFF0C;done&#x5C5E;&#x6027;&#x662F;&#x4E00;&#x4E2A;&#x5E03;&#x5C14;&#x503C;&#xFF0C;&#x8868;&#x793A;&#x904D;&#x5386;&#x662F;&#x5426;&#x7ED3;&#x675F;&#x3002;&#x4E0B;&#x9762;&#x662F;&#x4E00;&#x4E2A;&#x6A21;&#x62DF;next&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x503C;&#x7684;&#x4F8B;&#x5B50;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">makeIterator</span>(<span class="hljs-params">array</span>)</span>{
  <span class="hljs-keyword">var</span> nextIndex = <span class="hljs-number">0</span>;
  <span class="hljs-keyword">return</span> {
    next: <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params"></span>)</span>{
      <span class="hljs-keyword">return</span> nextIndex &lt; array.length ?
        {value: array[nextIndex++], done: <span class="hljs-literal">false</span>} :
        {value: <span class="hljs-literal">undefined</span>, done: <span class="hljs-literal">true</span>};
    }
  }
}

<span class="hljs-keyword">var</span> it = makeIterator([<span class="hljs-string">&apos;a&apos;</span>, <span class="hljs-string">&apos;b&apos;</span>]);

it.next() <span class="hljs-comment">// { value: &quot;a&quot;, done: false }</span>
it.next() <span class="hljs-comment">// { value: &quot;b&quot;, done: false }</span>
it.next() <span class="hljs-comment">// { value: undefined, done: true }</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x5B9A;&#x4E49;&#x4E86;&#x4E00;&#x4E2A;makeIterator&#x51FD;&#x6570;&#xFF0C;&#x5B83;&#x7684;&#x4F5C;&#x7528;&#x662F;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x904D;&#x5386;&#x5668;&#x5BF9;&#x8C61;&#xFF0C;&#x7528;&#x6765;&#x904D;&#x5386;&#x53C2;&#x6570;&#x6570;&#x7EC4;&#x3002;next&#x65B9;&#x6CD5;&#x4F9D;&#x6B21;&#x904D;&#x5386;&#x6570;&#x7EC4;&#x7684;&#x6BCF;&#x4E2A;&#x6210;&#x5458;&#xFF0C;&#x8BF7;&#x7279;&#x522B;&#x6CE8;&#x610F;&#xFF0C;next&#x8FD4;&#x56DE;&#x503C;&#x7684;&#x6784;&#x9020;&#x3002;</p>
<p>&#x4E0B;&#x9762;&#x662F;&#x4E00;&#x4E2A;&#x65E0;&#x9650;&#x8FD0;&#x884C;&#x7684;&#x904D;&#x5386;&#x5668;&#x4F8B;&#x5B50;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">idMaker</span>(<span class="hljs-params"></span>)</span>{
  <span class="hljs-keyword">var</span> index = <span class="hljs-number">0</span>;

  <span class="hljs-keyword">return</span> {
    next: <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params"></span>)</span>{
      <span class="hljs-keyword">return</span> {value: index++, done: <span class="hljs-literal">false</span>};
    }
  }
}

<span class="hljs-keyword">var</span> it = idMaker();

it.next().value <span class="hljs-comment">// &apos;0&apos;</span>
it.next().value <span class="hljs-comment">// &apos;1&apos;</span>
it.next().value <span class="hljs-comment">// &apos;2&apos;</span>
<span class="hljs-comment">// ...</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x7684;&#x4F8B;&#x5B50;&#xFF0C;&#x53EA;&#x662F;&#x4E3A;&#x4E86;&#x8BF4;&#x660E;next&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x503C;&#x7684;&#x7ED3;&#x6784;&#x3002;Iterator&#x63A5;&#x53E3;&#x8FD4;&#x56DE;&#x7684;&#x904D;&#x5386;&#x5668;&#xFF0C;&#x539F;&#x751F;&#x5177;&#x5907;next&#x65B9;&#x6CD5;&#xFF0C;&#x4E0D;&#x7528;&#x81EA;&#x5DF1;&#x90E8;&#x7F72;&#x3002;&#x6240;&#x4EE5;&#xFF0C;&#x771F;&#x6B63;&#x9700;&#x8981;&#x90E8;&#x7F72;&#x7684;&#x662F;Iterator&#x63A5;&#x53E3;&#xFF0C;&#x8BA9;&#x5176;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x904D;&#x5386;&#x5668;&#x3002;&#x5728;ES6&#x4E2D;&#xFF0C;&#x6709;&#x4E09;&#x7C7B;&#x6570;&#x636E;&#x7ED3;&#x6784;&#x539F;&#x751F;&#x5177;&#x5907;Iterator&#x63A5;&#x53E3;&#xFF1A;&#x6570;&#x7EC4;&#x3001;&#x7C7B;&#x4F3C;&#x6570;&#x7EC4;&#x7684;&#x5BF9;&#x8C61;&#x3001;Set&#x548C;Map&#x7ED3;&#x6784;&#x3002;&#x9664;&#x6B64;&#x4E4B;&#x5916;&#xFF0C;&#x5176;&#x4ED6;&#x6570;&#x636E;&#x7ED3;&#x6784;&#xFF08;&#x4E3B;&#x8981;&#x662F;&#x5BF9;&#x8C61;&#xFF09;&#x7684;Iterator&#x63A5;&#x53E3;&#x90FD;&#x9700;&#x8981;&#x81EA;&#x5DF1;&#x90E8;&#x7F72;&#x3002;</p>
<p>&#x4E0B;&#x9762;&#x5C31;&#x662F;&#x5982;&#x4F55;&#x90E8;&#x7F72;Iterator&#x63A5;&#x53E3;&#x3002;&#x4E00;&#x4E2A;&#x5BF9;&#x8C61;&#x5982;&#x679C;&#x8981;&#x6709;Iterator&#x63A5;&#x53E3;&#xFF0C;&#x5FC5;&#x987B;&#x90E8;&#x7F72;&#x4E00;&#x4E2A;@@iterator&#x65B9;&#x6CD5;&#xFF08;&#x539F;&#x578B;&#x94FE;&#x4E0A;&#x7684;&#x5BF9;&#x8C61;&#x5177;&#x6709;&#x8BE5;&#x65B9;&#x6CD5;&#x4E5F;&#x53EF;&#xFF09;&#xFF0C;&#x8BE5;&#x65B9;&#x6CD5;&#x90E8;&#x7F72;&#x5728;&#x4E00;&#x4E2A;&#x952E;&#x540D;&#x4E3A;<code>Symbol.iterator</code>&#x7684;&#x5C5E;&#x6027;&#x4E0A;&#xFF0C;&#x5BF9;&#x5E94;&#x7684;&#x952E;&#x503C;&#x662F;&#x4E00;&#x4E2A;&#x51FD;&#x6570;&#xFF0C;&#x8BE5;&#x51FD;&#x6570;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x904D;&#x5386;&#x5668;&#x5BF9;&#x8C61;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MySpecialTree</span> </span>{
  <span class="hljs-comment">// ...</span>
  [<span class="hljs-built_in">Symbol</span>.iterator]() { 
    <span class="hljs-comment">// ...</span>
    <span class="hljs-keyword">return</span> theIterator;
  }
}
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x662F;&#x4E00;&#x4E2A;&#x7C7B;&#x90E8;&#x7F72;Iterator&#x63A5;&#x53E3;&#x7684;&#x5199;&#x6CD5;&#x3002;<code>Symbol.iterator</code>&#x662F;&#x4E00;&#x4E2A;&#x8868;&#x8FBE;&#x5F0F;&#xFF0C;&#x8FD4;&#x56DE;Symbol&#x5BF9;&#x8C61;&#x7684;iterator&#x5C5E;&#x6027;&#xFF0C;&#x8FD9;&#x662F;&#x4E00;&#x4E2A;&#x9884;&#x5B9A;&#x4E49;&#x597D;&#x7684;&#x3001;&#x7C7B;&#x578B;&#x4E3A;Symbol&#x7684;&#x7279;&#x6B8A;&#x503C;&#xFF0C;&#x6240;&#x4EE5;&#x8981;&#x653E;&#x5728;&#x65B9;&#x62EC;&#x53F7;&#x5185;&#xFF08;&#x8BF7;&#x53C2;&#x8003;Symbol&#x4E00;&#x8282;&#xFF09;&#x3002;&#x8FD9;&#x91CC;&#x8981;&#x6CE8;&#x610F;&#xFF0C;@@iterator&#x7684;&#x952E;&#x540D;&#x662F;<code>Symbol.iterator</code>&#xFF0C;&#x952E;&#x503C;&#x662F;&#x4E00;&#x4E2A;&#x65B9;&#x6CD5;&#xFF08;&#x51FD;&#x6570;&#xFF09;&#xFF0C;&#x8BE5;&#x65B9;&#x6CD5;&#x6267;&#x884C;&#x540E;&#xFF0C;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x5F53;&#x524D;&#x5BF9;&#x8C61;&#x7684;&#x904D;&#x5386;&#x5668;&#x3002;</p>
<p>&#x4E0B;&#x9762;&#x662F;&#x4E3A;&#x5BF9;&#x8C61;&#x6DFB;&#x52A0;Iterator&#x63A5;&#x53E3;&#x7684;&#x4F8B;&#x5B50;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">let</span> obj = {
  data: [ <span class="hljs-string">&apos;hello&apos;</span>, <span class="hljs-string">&apos;world&apos;</span> ],
  [<span class="hljs-built_in">Symbol</span>.iterator]() {
    <span class="hljs-keyword">const</span> self = <span class="hljs-keyword">this</span>;
    <span class="hljs-keyword">let</span> index = <span class="hljs-number">0</span>;
    <span class="hljs-keyword">return</span> {
      next() {
        <span class="hljs-keyword">if</span> (index &lt; self.data.length) {
          <span class="hljs-keyword">return</span> {
            value: self.data[index++],
            done: <span class="hljs-literal">false</span>
          };
        } <span class="hljs-keyword">else</span> {
          <span class="hljs-keyword">return</span> { value: <span class="hljs-literal">undefined</span>, done: <span class="hljs-literal">true</span> };
        }
      }
    };
  }
};
</code></pre>
<p>&#x300A;&#x6570;&#x7EC4;&#x7684;&#x6269;&#x5C55;&#x300B;&#x4E00;&#x7AE0;&#x4E2D;&#x63D0;&#x5230;&#xFF0C;ES6&#x5BF9;&#x6570;&#x7EC4;&#x63D0;&#x4F9B;entries()&#x3001;keys()&#x548C;values()&#x4E09;&#x4E2A;&#x65B9;&#x6CD5;&#xFF0C;&#x5C31;&#x662F;&#x8FD4;&#x56DE;&#x4E09;&#x4E2A;&#x904D;&#x5386;&#x5668;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">var</span> arr = [<span class="hljs-number">1</span>, <span class="hljs-number">5</span>, <span class="hljs-number">7</span>];
<span class="hljs-keyword">var</span> arrEntries = arr.entries();

arrEntries.toString() 
<span class="hljs-comment">// &quot;[object Array Iterator]&quot;</span>

arrEntries === arrEntries[<span class="hljs-built_in">Symbol</span>.iterator]()
<span class="hljs-comment">// true</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;entries&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x662F;&#x4E00;&#x4E2A;&#x904D;&#x5386;&#x5668;&#xFF08;iterator&#xFF09;&#xFF0C;&#x672C;&#x8D28;&#x4E0A;&#x5C31;&#x662F;&#x8C03;&#x7528;&#x4E86;<code>Symbol.iterator</code>&#x65B9;&#x6CD5;&#x3002;</p>
<p>&#x5B57;&#x7B26;&#x4E32;&#x662F;&#x4E00;&#x4E2A;&#x7C7B;&#x4F3C;&#x6570;&#x7EC4;&#x7684;&#x5BF9;&#x8C61;&#xFF0C;&#x56E0;&#x6B64;&#x4E5F;&#x539F;&#x751F;&#x5177;&#x6709;Iterator&#x63A5;&#x53E3;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">var</span> someString = <span class="hljs-string">&quot;hi&quot;</span>;
<span class="hljs-keyword">typeof</span> someString[<span class="hljs-built_in">Symbol</span>.iterator] 
<span class="hljs-comment">// &quot;function&quot;</span>

<span class="hljs-keyword">var</span> iterator = someString[<span class="hljs-built_in">Symbol</span>.iterator]();

iterator.next()  <span class="hljs-comment">// { value: &quot;h&quot;, done: false }</span>
iterator.next()  <span class="hljs-comment">// { value: &quot;i&quot;, done: false }</span>
iterator.next()  <span class="hljs-comment">// { value: undefined, done: true }</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;&#x8C03;&#x7528;<code>Symbol.iterator</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x904D;&#x5386;&#x5668;&#xFF0C;&#x5728;&#x8FD9;&#x4E2A;&#x904D;&#x5386;&#x5668;&#x4E0A;&#x53EF;&#x4EE5;&#x8C03;&#x7528;next&#x65B9;&#x6CD5;&#xFF0C;&#x5B9E;&#x73B0;&#x5BF9;&#x4E8E;&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x904D;&#x5386;&#x3002;</p>
<p>&#x53EF;&#x4EE5;&#x8986;&#x76D6;&#x539F;&#x751F;&#x7684;<code>Symbol.iterator</code>&#x65B9;&#x6CD5;&#xFF0C;&#x8FBE;&#x5230;&#x4FEE;&#x6539;&#x904D;&#x5386;&#x5668;&#x884C;&#x4E3A;&#x7684;&#x76EE;&#x7684;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">var</span> str = <span class="hljs-keyword">new</span> <span class="hljs-built_in">String</span>(<span class="hljs-string">&quot;hi&quot;</span>);

[...str] <span class="hljs-comment">// [&quot;h&quot;, &quot;i&quot;]</span>

str[<span class="hljs-built_in">Symbol</span>.iterator] = <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params"></span>) </span>{
  <span class="hljs-keyword">return</span> { 
    next: <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params"></span>) </span>{
      <span class="hljs-keyword">if</span> (<span class="hljs-keyword">this</span>._first) {
        <span class="hljs-keyword">this</span>._first = <span class="hljs-literal">false</span>;
        <span class="hljs-keyword">return</span> { value: <span class="hljs-string">&quot;bye&quot;</span>, done: <span class="hljs-literal">false</span> };
      } <span class="hljs-keyword">else</span> {
        <span class="hljs-keyword">return</span> { done: <span class="hljs-literal">true</span> };
      }
    },
    _first: <span class="hljs-literal">true</span>
  };
};

[...str] <span class="hljs-comment">// [&quot;bye&quot;]  </span>
str <span class="hljs-comment">// &quot;hi&quot;</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;&#x5B57;&#x7B26;&#x4E32;str&#x7684;<code>Symbol.iterator</code>&#x65B9;&#x6CD5;&#x88AB;&#x4FEE;&#x6539;&#x4E86;&#xFF0C;&#x6240;&#x4EE5;&#x6269;&#x5C55;&#x8FD0;&#x7B97;&#x7B26;&#xFF08;...&#xFF09;&#x8FD4;&#x56DE;&#x7684;&#x503C;&#x53D8;&#x6210;&#x4E86;bye&#xFF0C;&#x800C;&#x5B57;&#x7B26;&#x4E32;&#x672C;&#x8EAB;&#x8FD8;&#x662F;hi&#x3002;</p>
<p>&#x90E8;&#x7F72;<code>Symbol.iterator</code>&#x65B9;&#x6CD5;&#x7684;&#x6700;&#x7B80;&#x5355;&#x5B9E;&#x73B0;&#xFF0C;&#x8FD8;&#x662F;&#x4F7F;&#x7528;&#x4E0B;&#x4E00;&#x8282;&#x8981;&#x63D0;&#x5230;&#x7684;Generator&#x51FD;&#x6570;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">var</span> myIterable = {};

myIterable[<span class="hljs-built_in">Symbol</span>.iterator] = <span class="hljs-function"><span class="hljs-keyword">function</span>* (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">yield</span> <span class="hljs-number">1</span>;
    <span class="hljs-keyword">yield</span> <span class="hljs-number">2</span>;
    <span class="hljs-keyword">yield</span> <span class="hljs-number">3</span>;
};
[...myIterable] <span class="hljs-comment">// [1, 2, 3]</span>

<span class="hljs-comment">// &#x6216;&#x8005;&#x91C7;&#x7528;&#x4E0B;&#x9762;&#x7684;&#x7B80;&#x6D01;&#x5199;&#x6CD5;</span>

<span class="hljs-keyword">let</span> obj = {
  * [<span class="hljs-built_in">Symbol</span>.iterator]() {
    <span class="hljs-keyword">yield</span> <span class="hljs-string">&apos;hello&apos;</span>;
    <span class="hljs-keyword">yield</span> <span class="hljs-string">&apos;world&apos;</span>;
  }
};

<span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> x <span class="hljs-keyword">of</span> obj) {
  <span class="hljs-built_in">console</span>.log(x);
}
<span class="hljs-comment">// hello</span>
<span class="hljs-comment">// world</span>
</code></pre>
<p>&#x5982;&#x679C;<code>Symbol.iterator</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x4E0D;&#x662F;&#x904D;&#x5386;&#x5668;&#xFF0C;&#x89E3;&#x91CA;&#x5F15;&#x64CE;&#x5C06;&#x4F1A;&#x62A5;&#x9519;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">var</span> obj = {};

obj[<span class="hljs-built_in">Symbol</span>.iterator] = () =&gt; <span class="hljs-number">1</span>;

[...obj] <span class="hljs-comment">// TypeError: [] is not a function</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;&#x53D8;&#x91CF;obj&#x7684;@@iterator&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x4E0D;&#x662F;&#x904D;&#x5386;&#x5668;&#xFF0C;&#x56E0;&#x6B64;&#x62A5;&#x9519;&#x3002;</p>
<h2 id="for-of%E5%BE%AA%E7%8E%AF">for...of&#x5FAA;&#x73AF;</h2>
<p>ES6&#x4E2D;&#xFF0C;&#x4E00;&#x4E2A;&#x5BF9;&#x8C61;&#x53EA;&#x8981;&#x90E8;&#x7F72;&#x4E86;@@iterator&#x65B9;&#x6CD5;&#xFF0C;&#x5C31;&#x88AB;&#x89C6;&#x4E3A;&#x5177;&#x6709;iterator&#x63A5;&#x53E3;&#xFF0C;&#x5C31;&#x53EF;&#x4EE5;&#x7528;for...of&#x5FAA;&#x73AF;&#x904D;&#x5386;&#x5B83;&#x7684;&#x503C;&#x3002;&#x4E5F;&#x5C31;&#x662F;&#x8BF4;&#xFF0C;for...of&#x5FAA;&#x73AF;&#x5185;&#x90E8;&#x8C03;&#x7528;&#x662F;&#x539F;&#x5BF9;&#x8C61;&#x7684;<code>Symbol.iterator</code>&#x65B9;&#x6CD5;&#x3002;</p>
<p>&#x6570;&#x7EC4;&#x539F;&#x751F;&#x5177;&#x5907;iterator&#x63A5;&#x53E3;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">const</span> arr = [<span class="hljs-string">&apos;red&apos;</span>, <span class="hljs-string">&apos;green&apos;</span>, <span class="hljs-string">&apos;blue&apos;</span>];

<span class="hljs-keyword">for</span>(<span class="hljs-keyword">let</span> v <span class="hljs-keyword">of</span> arr) {
    <span class="hljs-built_in">console</span>.log(v); <span class="hljs-comment">// red green blue</span>
}
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x8BF4;&#x660E;&#xFF0C;for...of&#x5FAA;&#x73AF;&#x53EF;&#x4EE5;&#x4EE3;&#x66FF;&#x6570;&#x7EC4;&#x5B9E;&#x4F8B;&#x7684;forEach&#x65B9;&#x6CD5;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">const</span> arr = [<span class="hljs-string">&apos;red&apos;</span>, <span class="hljs-string">&apos;green&apos;</span>, <span class="hljs-string">&apos;blue&apos;</span>];

arr.forEach(<span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params">element, index</span>) </span>{
    <span class="hljs-built_in">console</span>.log(element); <span class="hljs-comment">// red green blue</span>
    <span class="hljs-built_in">console</span>.log(index);   <span class="hljs-comment">// 0 1 2</span>
});
</code></pre>
<p>JavaScript&#x539F;&#x6709;&#x7684;for...in&#x5FAA;&#x73AF;&#xFF0C;&#x53EA;&#x80FD;&#x83B7;&#x5F97;&#x5BF9;&#x8C61;&#x7684;&#x952E;&#x540D;&#xFF0C;&#x4E0D;&#x80FD;&#x76F4;&#x63A5;&#x83B7;&#x53D6;&#x952E;&#x503C;&#x3002;ES6&#x63D0;&#x4F9B;for...of&#x5FAA;&#x73AF;&#xFF0C;&#x5141;&#x8BB8;&#x904D;&#x5386;&#x83B7;&#x5F97;&#x952E;&#x503C;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">var</span> arr = [<span class="hljs-string">&quot;a&quot;</span>, <span class="hljs-string">&quot;b&quot;</span>, <span class="hljs-string">&quot;c&quot;</span>, <span class="hljs-string">&quot;d&quot;</span>];
<span class="hljs-keyword">for</span> (a <span class="hljs-keyword">in</span> arr) {
  <span class="hljs-built_in">console</span>.log(a); <span class="hljs-comment">// 0 1 2 3</span>
}

<span class="hljs-keyword">for</span> (a <span class="hljs-keyword">of</span> arr) {
  <span class="hljs-built_in">console</span>.log(a); <span class="hljs-comment">// a b c d</span>
}
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x8868;&#x660E;&#xFF0C;for...in&#x5FAA;&#x73AF;&#x8BFB;&#x53D6;&#x952E;&#x540D;&#xFF0C;for...of&#x5FAA;&#x73AF;&#x8BFB;&#x53D6;&#x952E;&#x503C;&#x3002;&#x5982;&#x679C;&#x8981;&#x901A;&#x8FC7;for...of&#x5FAA;&#x73AF;&#xFF0C;&#x83B7;&#x53D6;&#x6570;&#x7EC4;&#x7684;&#x7D22;&#x5F15;&#xFF0C;&#x53EF;&#x4EE5;&#x501F;&#x52A9;&#x6570;&#x7EC4;&#x5B9E;&#x4F8B;&#x7684;entries&#x65B9;&#x6CD5;&#x548C;keys&#x65B9;&#x6CD5;&#xFF0C;&#x53C2;&#x89C1;&#x300A;&#x6570;&#x7EC4;&#x7684;&#x6269;&#x5C55;&#x300B;&#x7AE0;&#x8282;&#x3002;</p>
<p>Set&#x548C;Map&#x7ED3;&#x6784;&#x4E5F;&#x539F;&#x751F;&#x5177;&#x6709;Iterator&#x63A5;&#x53E3;&#xFF0C;&#x53EF;&#x4EE5;&#x76F4;&#x63A5;&#x4F7F;&#x7528;for...of&#x5FAA;&#x73AF;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">var</span> engines = <span class="hljs-built_in">Set</span>([<span class="hljs-string">&quot;Gecko&quot;</span>, <span class="hljs-string">&quot;Trident&quot;</span>, <span class="hljs-string">&quot;Webkit&quot;</span>, <span class="hljs-string">&quot;Webkit&quot;</span>]);
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> e <span class="hljs-keyword">of</span> engines) {
    <span class="hljs-built_in">console</span>.log(e);
}
<span class="hljs-comment">// Gecko</span>
<span class="hljs-comment">// Trident</span>
<span class="hljs-comment">// Webkit</span>

<span class="hljs-keyword">var</span> es6 = <span class="hljs-keyword">new</span> <span class="hljs-built_in">Map</span>();
es6.set(<span class="hljs-string">&quot;edition&quot;</span>, <span class="hljs-number">6</span>);
es6.set(<span class="hljs-string">&quot;committee&quot;</span>, <span class="hljs-string">&quot;TC39&quot;</span>);
es6.set(<span class="hljs-string">&quot;standard&quot;</span>, <span class="hljs-string">&quot;ECMA-262&quot;</span>);
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">var</span> [name, value] <span class="hljs-keyword">of</span> es6) {
  <span class="hljs-built_in">console</span>.log(name + <span class="hljs-string">&quot;: &quot;</span> + value);
}
<span class="hljs-comment">// edition: 6</span>
<span class="hljs-comment">// committee: TC39</span>
<span class="hljs-comment">// standard: ECMA-262</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x6F14;&#x793A;&#x4E86;&#x5982;&#x4F55;&#x904D;&#x5386;Set&#x7ED3;&#x6784;&#x548C;Map&#x7ED3;&#x6784;&#xFF0C;&#x540E;&#x8005;&#x662F;&#x540C;&#x65F6;&#x904D;&#x5386;&#x952E;&#x540D;&#x548C;&#x952E;&#x503C;&#x3002;</p>
<p>&#x5BF9;&#x4E8E;&#x666E;&#x901A;&#x7684;&#x5BF9;&#x8C61;&#xFF0C;for...of&#x7ED3;&#x6784;&#x4E0D;&#x80FD;&#x76F4;&#x63A5;&#x4F7F;&#x7528;&#xFF0C;&#x4F1A;&#x62A5;&#x9519;&#xFF0C;&#x5FC5;&#x987B;&#x90E8;&#x7F72;&#x4E86;iterator&#x63A5;&#x53E3;&#x540E;&#x624D;&#x80FD;&#x4F7F;&#x7528;&#x3002;&#x4F46;&#x662F;&#xFF0C;&#x8FD9;&#x6837;&#x60C5;&#x51B5;&#x4E0B;&#xFF0C;for...in&#x5FAA;&#x73AF;&#x4F9D;&#x7136;&#x53EF;&#x4EE5;&#x7528;&#x6765;&#x904D;&#x5386;&#x952E;&#x540D;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-keyword">var</span> es6 = {
  edition: <span class="hljs-number">6</span>,
  committee: <span class="hljs-string">&quot;TC39&quot;</span>,
  standard: <span class="hljs-string">&quot;ECMA-262&quot;</span>
};

<span class="hljs-keyword">for</span> (e <span class="hljs-keyword">in</span> es6) {
  <span class="hljs-built_in">console</span>.log(e);
}
<span class="hljs-comment">// edition</span>
<span class="hljs-comment">// committee</span>
<span class="hljs-comment">// standard</span>

<span class="hljs-keyword">for</span> (e <span class="hljs-keyword">of</span> es6) {
  <span class="hljs-built_in">console</span>.log(e);
}
<span class="hljs-comment">// TypeError: es6 is not iterable</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x8868;&#x793A;&#xFF0C;for...in&#x5FAA;&#x73AF;&#x53EF;&#x4EE5;&#x904D;&#x5386;&#x952E;&#x540D;&#xFF0C;for...of&#x5FAA;&#x73AF;&#x4F1A;&#x62A5;&#x9519;&#x3002;</p>
<p>&#x603B;&#x7ED3;&#x4E00;&#x4E0B;&#xFF0C;for...of&#x5FAA;&#x73AF;&#x53EF;&#x4EE5;&#x4F7F;&#x7528;&#x7684;&#x8303;&#x56F4;&#x5305;&#x62EC;&#x6570;&#x7EC4;&#x3001;&#x7C7B;&#x4F3C;&#x6570;&#x7EC4;&#x7684;&#x5BF9;&#x8C61;&#xFF08;&#x6BD4;&#x5982;arguments&#x5BF9;&#x8C61;&#x3001;DOM NodeList&#x5BF9;&#x8C61;&#xFF09;&#x3001;Set&#x548C;Map&#x7ED3;&#x6784;&#x3001;&#x540E;&#x6587;&#x7684;Generator&#x5BF9;&#x8C61;&#xFF0C;&#x4EE5;&#x53CA;&#x5B57;&#x7B26;&#x4E32;&#x3002;&#x4E0B;&#x9762;&#x662F;for...of&#x5FAA;&#x73AF;&#x7528;&#x4E8E;&#x5B57;&#x7B26;&#x4E32;&#x548C;DOM NodeList&#x5BF9;&#x8C61;&#x7684;&#x4F8B;&#x5B50;&#x3002;</p>
<pre><code class="lang-javascript">
<span class="hljs-comment">// &#x5B57;&#x7B26;&#x4E32;&#x7684;&#x4F8B;&#x5B50;</span>

<span class="hljs-keyword">let</span> str = <span class="hljs-string">&quot;hello&quot;</span>;

<span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> s <span class="hljs-keyword">of</span> str) {
  <span class="hljs-built_in">console</span>.log(s); <span class="hljs-comment">// h e l l o</span>
}

<span class="hljs-comment">// DOM NodeList&#x5BF9;&#x8C61;&#x7684;&#x4F8B;&#x5B50;</span>

<span class="hljs-keyword">let</span> paras = <span class="hljs-built_in">document</span>.querySelectorAll(<span class="hljs-string">&quot;p&quot;</span>);

<span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> p <span class="hljs-keyword">of</span> paras) {
  p.classList.add(<span class="hljs-string">&quot;test&quot;</span>);
}
</code></pre>

                    
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